This invention relates to methods of joining two metal members by utilizing plastic deformation, and more particularly it is concerned with a joining method suitable for use in rigidly securing metal members, such as shafts, cylinders, disks, etc., to each other.
In one method of joining two metal members to each other known in the art, an annular groove is formed on each of the metal members and a metal ring is force fitted between the two metal members to cause part of the metal ring to undergo plastic deformation and flow into the grooves in the metal members. The art described is disclosed in U.S. Pat. No. 3,559,946 and U.S. Pat. No. 2,804,679, for example.
This joining method has the advantage of imparting higher shear strength to the joint than a method of joining two metal members together merely by force fitting. However, the methods disclosed in the documents referred to hereinabove have been carried into practice for joining stationary members to each other, and no attempts have ever been made to apply the art to joining of metal members transmitting a torque. When the metal members transmit a torque, the joint provided by joining them should have higher shear strength or torsional strength than the joint formed by joining members that do not transmit a torque. The results of experiments conducted by us show that it is impossible to obtain sufficiently high strength with which the two metal members are joined to each other merely by increasing the dimensions of the grooves or increasing the depth and width of the grooves or by increasing the number of grooves. These measures are intended to increase the volume of metallic material flowing into the grooves. However, when these measures are adopted, no satisfactory results could be achieved because the distance of movement of the metallic material increases and this would cause an increase in frictional loss occurring when a metallic material flows. Thus even if higher pressure is applied, it would be impossible to obtain satisfactory inflow of the metallic material into the grooves, and voids would be present in the grooves. As a result, the strength with which the two metal members are joined would not increase and a potential source of corrosion would be formed. An increase in the pressure with which joining is effected would cause those parts of the metal members which do not concern in joining to undergo plastic deformation, thereby making dimensional accuracy of the product unobtainable.